use half raspberries half rhubard. it may be one of those jams that takes a while to set. ALSO pectin is very very time confined. If you over cook a jam you actually cook the pectin out of it so cooking it beyond the set time may not be a good thing. if in two weeks your jam has not set you can recook it again with more pectin following the rules of the pectin. Rhubarb has a LOT of water in it so its a thinner product once cooked down anyways and I always use canned diced pineapple in my apricot jams and it sets fine. I just made some rhubarb chipotle marinade with Jaba and it had raspberries and rhubarb onions garlic and diced chipotle in adobo sauce and it came out marvelous. We canned that and use it on bbq stuff.